An endotracheal tube, or similar airway device, is used to maintain a clear airway in a patient, e.g. for artificial ventilation during surgery. Typically, the device includes an inflatable cuff, which is inflated when in position in a patient's airway. The inflated cuff forms a seal, between the airway device and the tissues surrounding the airway, to thereby maintain the device in position in a patient's airway, and to prevent leakage of infected oropharyngeal secretions into the patient's lungs.
WO-A-99/33508 describes an apparatus that includes a monitoring system for monitoring pressure in the cuff of a laryngeal mask airway device, and for maintaining the inflated cuff at a preset pressure, within narrow tolerances. In particular, the apparatus periodically measures the pressure within a closed system incorporating the inflated cuff and compares the measured pressure with a preset pressure, to determine a difference and its polarity. The apparatus then controls the pressure within the closed system to reduce the difference to zero. The disclosure of WO-A-99/33508 is incorporated herein, by reference.